Effect of Maturation on the Osteogenic Response of Cultured
Stromal Bone Marrow Cells to Basic Fibroblast
Growth Factor
S. KOTEV-EMETH,
1
N. SAVION,
1
S. PRI-CHEN,
1
and S. PITARU
2
1
Maurice and Gabriela Goldschleger Eye Research Institute, and
2
Department of Oral Biology, Maurice and Gabriela Goldschleger School of
Dental Medicine, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
Formation of bone-like tissue in culture by stromal bone
marrow cells (SBMC) derived from young growing rats is
dependent on dexamethasone (Dex) (Cell Tissue Res 254:317;
1988) and is significantly enhanced by basic fibroblast
growth factor (bFGF) (J Bone Miner Res 8:919; 1993). The
aim of this study was to examine the effect of maturation on
the osteogenic potential and the response to Dex and bFGF of
SBMC by using cultures derived from young growing (6
weeks old) and adult (9 months old) rats. SBMC cultures
were grown in the presence of Dex (10
؊8
or 10
؊7
mol/L) at
both P
0
and P
1
and either in the presence or absence of
bFGF. The effect of Dex and bFGF on mineralized bone-like
tissue (MBT) formation was assessed at P
1
. The highest levels
of mineralized tissue formation in P
1
subcultures in the
absence of bFGF were obtained when cultures derived from
young rats (6 weeks old) were treated with Dex 10
؊7
and
10
؊8
mol/L at P
0
and P
1
, respectively, and when cultures
derived from adult rats were exposed to Dex 10
؊8
mol/L both
at P
0
and P
1
. Under these optimal Dex concentrations, the
amount of MBT formed by adult rat-derived cultures was
15-fold lower than that of young rat-derived ones. The addi-
tion of bFGF to P
0
cultures or to P
1
cultures grown under
optimal Dex conditions enhanced MBT formation in P
1
cul-
tures derived from both young and adult rats, but this effect
was considerably more pronounced in the adult rat-derived
cultures. The maximal levels of MBT formation were pro-
duced by cultures derived from adult rats treated with bFGF
at both P
0
and P
1
, whereas in cultures derived from young
rats, the addition of bFGF at P
0
was not necessary for
maximal MBT production. This stimulating effect of bFGF
on MBT formation by adult rat-derived cultures was accom-
panied by a 2.2-, 1.8-, and 4.3-fold increase in proliferation,
alkaline phosphatase activity, and Ca
2؉
deposition rate, re-
spectively. bFGF increased the level of glucocorticoid recep-
tor by approximately 2.3-fold in Dex-treated cultures derived
from young animals. These results indicate that maturation is
associated with a decrease in the proportion of osteoprogeni-
tor cells in the stromal bone marrow and in their capacity to
express the osteogenic phenotype. They further point to the
significant role of bFGF in stimulating proliferation and
osteogenic expression of stromal bone marrow osteoprogeni-
tors derived from adult rats. (Bone 27:777–783; 2000)
© 2000 by Elsevier Science Inc. All rights reserved.
Key Words: Maturation; bFGF; Bone cells; Osteoblast; Stromal
bone-marrow cells; Dexamethasone.
Introduction
Maturation and aging are accompanied by a reduction in bone
mass consequent to an imbalance between bone formation and
resorption during the remodeling process.
26,31,32,37
In vivo stud-
ies demonstrate an age-related decline in the stromal cell volume,
the osteoblast number per unit bone length, osteoid volume,
osteoblastic surface and mineralized surface, and an increase in
osteoclast number.
10,26,31–33
Demineralized bone matrix from
aged rats demonstrates a reduced potential to induce bone for-
mation.
24
Bone marrow cell cultures derived from aged rats have
been shown to produce less bone-like nodules, fibroblastic col-
ony forming units, and adherent cells with osteoblastic charac-
teristics than cultures derived from growing and adult rats,
suggesting an aged-related decrease in the osteoprogenitor cell
population present in bone marrow.
9,17,31,37
Moreover, a reduc-
tion was shown in the expression of osteoblastic markers by cells
derived from aged compared with those expressed by cells
derived from young rats.
9,37
Bone formation and remodeling
involve the recruitment of osteoprogenitor cells from the bone
marrow cells population, their proliferation, and terminal differ-
entiation into active osteoblasts. It has been established that these
processes are highly regulated by systemic osteotropic hor-
mones
4,6,22
and by growth factors.
5
Growth factors are produced
by bone cells and accumulate in the bone matrix,
16,38
thus locally
acting on osteoprogenitor cells and modulating their proliferation
and differentiation along the bone modeling pathway. In recent
studies, the role of insulin-like growth factor (IGF-I) and trans-
forming growth factor-beta (TGF-) in bone remodeling
22,38
has
been demonstrated. An age-related decrease was observed in
IGF-I and TGF- content of cortical bone of both men and
women,
23
as well as in the responsiveness of bone cultures to
parathyroid hormone (PTH) and to IGF-I, TGF-, and platelet-
derived growth factor (PDGF-BB).
7,11,28,34
This finding suggests
that the reduced number of osteoprogenitors in the bone marrow
of the aged organism is consequent to a decrease in the avail-
ability of growth factors in their microenvironment and/or a
decrease in responsiveness to hormones and growth factors.
bFGF is produced by bone cells
13,16
and stored in bone
Address for correspondence and reprints: Prof. Sandu Pitaru, Depart-
ment of Oral Biology, Maurice and Gabriela Goldschleger School of
Dental Medicine, Tel Aviv University, Tel Aviv 69970, Israel. E-mail:
pitaru@post.tau.ac.il
Bone Vol. 27, No. 6
December 2000:777–783
777
© 2000 by Elsevier Science Inc. 8756-3282/00/$20.00
All rights reserved. PII S8756-3282(00)00389-6